drm/i915/gt: Double check heartbeat timeout before resetting

Check that we have actually passed the heartbeat interval since last
checking the request before resetting the device.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2780


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210204211303.21347-2-chris@chris-wilson.co.uk


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>